On the following day, all the junk is in the
bottom of the flask and the gold solution is ready to be filtered. It is highly recommend using a proper laboratory
filters and not store bought coffee filters. I'm using medium-slow speed filters, which
will strain any solid particle over 5 microns. The fluted filter paper sets in the funnel
as soon as it gets wet. First, the bulk of the gold solution which
is free and clear of solid particles is poured to the filter. This portion will run down
very fast. Here in the flask you can see the remaining
junk, I'll just wash it several times with water and pour it down the filter. The bulk
of the solids are left in the flask. Please remember to wash the filter with plenty
of water so that all of the yellow gold bearing solution will run down to the receiving flask. When you are done, the filter should be white
again. Our next step is to remove the gold from the
solution. This is done by using Sodium Meta-bisulfite
or in short S.M.B., The S.M.B is first dissolved in water and then added to a stirred Gold
solution. The S.M.B will react with the Gold ions in
the solution and reduce it to metallic gold powder. As a result, some Sulfur Dioxide gas will release... It's
pretty toxic so the reaction must be done under a fume-hood. Btw, you don't really have to use a magnetic
stirrer like in this video, it is just my personal favorite. The solution is again left to settle overnight Here you can see the gold powder all settled
to the bottom of the flask and the supernatant is practically colorless. This is a good indication
for purity. The bulk of the solution is slowly decanted
and the washing cycles begin. The washing cycles are extremely important
if commercially pure gold is wanted. Starting with simple tap water wash... The
Gold powder is covered with boiling hot water, swirled for a while and left cool back down. This water wash is repeated two more times. Take note of the color of the Gold powder
prior to the acid wash. Now for the acid wash, the powder is simply
covered with Hydrochloric acid 32% and brought to a gentle boil. Take note of the color of the solution...
The acid dissolve traces of Copper, Nickel and silver chloride and it will also dissolve
some Gold. The acid wash is left to cool down and later
decanted. The process is repeated until the acid wash doesn't gain any color anymore. It usually takes three to five washes. In between each acid wash, it will be a good
idea to do a quick water wash so that a better indication of color change can be seen on
the next wash. I like to keep the acid washes in a separate
container and use it later to dissolve more dirty Gold. Take a close look on the powder after the
acid washes... The color is clearly lighter. Which is another good indication for purity. The powder is later washed several times with
Distilled water and placed on a hot plated to slowly dry out. And here's the result. I hope you found this demonstration useful
and interesting... Please comment, Share and Subscribe. Oh... by the way, click here to jump over
to the melting video...